The basic molecular and biological mechanisms involved in the vascular response to injury have yet to be clearly defined. Convergence of findings from several lines of studies in the laboratory of the P.I. has led to an emerging new model which suggests that cationic amino acid (L- arginine, L-ornithine) transport and metabolism are critical processes in modulating the response to vascular injury. The basic hypothesis of this proposed project is that biochemical mediators (growth factors, cytokines), hemodynamic forces (shear stress, cyclic stretch), and injury all act as stimuli of cationic amino acid transport in vascular smooth muscle cells (SMC) but exert highly selective and divergent actions on the intracellular pathways of L-arginine and L-ornithine metabolism. Further, it is proposed that these pathways are critical regulators of the major processes of vascular remodeling, including SMC proliferation and extracellular matrix collagen synthesis: L-ornithine- derived polyamines and L-proline promote these activities, while L- arginine-derived nitric oxide inhibits them. This project will study this problem and further develop this new model utilizing three linked specific aims that utilize complementary in vitro and in vivo approaches. First, experiments are designed to elucidate the control of L-arginine/L-ornithine transport and metabolism by growth factors and cytokines in cultured SMC. Studies will examine the growth factor and cytokine control of the functions and gene expression of vascular SMC cationic amino acid transporters (CATs), and the L-ornithine- metabolizing enzymes, ornithine decarboxylase and aminotransferase. Second, studies are proposed to examine the effect of the more complex, pathophysiologically relevant hemodynamic stimuli of cyclic stretch and shear stress on vascular SMC L-arginine/L-ornithine transport and metabolism. Third, these in vitro findings will be applied to an in vivo-model of vascular injury. Experiments will be performed to study the regulation of L-arginine/L-ornithine transport and metabolism, including their roles in SMC proliferation and extracellular matrix collagen synthesis, using a well characterized model of arterial injury in mice. Using pharmacologic, and ultimately transgenic approaches, this model should help define the biological roles of SMC cationic amino acid transport and metabolism in vascular remodeling in vivo. Elucidation of the molecular mechanisms that modulate the response to vascular injury will provide new rational targets for therapeutic intervention.